CRUD - 无法更新插入的数据javabeans，servlet

Question

我开发了一个CRUD应用程序，它正在运行，但我无法更新已插入的数据。这是我的代码，告诉我是否需要任何其他文件.. 我没有得到任何错误..... 所以我无法找到问题出在哪里......

UserHandler.java

package handler;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

import dao.UserDao;
import bean.UserBean;

public class UserHandler extends HttpServlet    {
    private static String INSERT = "/user.jsp";
    private static String Edit = "/edit.jsp";
    private static String UserRecord = "/listUser.jsp";
    private UserDao dao;

    public UserHandler()    {
        this.dao = new UserDao();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException    {
        String redirect = "";
        String roll = request.getParameter("rollno");
        String mo = request.getParameter("mono");
        String action = request.getParameter("action");

        if (action.equalsIgnoreCase("insert"))  {
//      if (action.equalsIgnoreCase("insert"))  {
//      if ((roll != null) && (action.equalsIgnoreCase("insert")))  {
            int rollno = Integer.parseInt(roll);
            long mono = Integer.parseInt(mo);
            UserBean user = new UserBean();
            user.setName(request.getParameter("name"));
            user.setRollno(rollno);
            user.setClas(request.getParameter("clas"));
            user.setMono(mono);
            this.dao.addUser(user);
            redirect = UserRecord;
            request.setAttribute("student", this.dao.getAllUsers());
            System.out.println("Record Added Successfully");
        }
        else if (action.equalsIgnoreCase("delete")) {
            int rollno = Integer.parseInt(roll);
            this.dao.removeUser(rollno);
            redirect = UserRecord;
            request.setAttribute("student", this.dao.getAllUsers());
            System.out.println("Record Deleted Successfully");
        }
        else if (action.equalsIgnoreCase("editform")) {
            redirect = Edit;
        }
        else if (action.equalsIgnoreCase("edit")) {
            int rollno = Integer.parseInt(roll);
            long mono = Long.parseLong(mo);

            UserBean user = new UserBean();
            user.setName(request.getParameter("name"));
            user.setRollno(rollno);
            user.setClas(request.getParameter("clas"));
            user.setMono(mono);
            this.dao.editUser(user);
            request.setAttribute("student", this.dao.getAllUsers());
            redirect = UserRecord;
            System.out.println("Record updated Successfully");
        }
        else if (action.equalsIgnoreCase("listUser")) {
            redirect = UserRecord;
            request.setAttribute("student", this.dao.getAllUsers());
        }
        else {
            redirect = INSERT;
        }

        RequestDispatcher rd = request.getRequestDispatcher(redirect);
        rd.forward(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException {
        doGet(request, response);
    }
}

UserDao.java

package dao;

import java.sql.*;
import java.util.*;

import dbconnection.ConnectionProvider;
import bean.UserBean;

public class UserDao    {
    private Connection con;


    public UserDao() { 
        this.con = ConnectionProvider.getConnection(); 
        System.out.println("Value of conn is  "+con);  
    }

/*  public UserDao()    {
        this.conn = ConnectionProvider.getConnection();
    }
*/  



// Insert Data  
    public void addUser(UserBean userBean) {
        try {
            String sql = "INSERT INTO student (name, rollno, class, mobileno) VALUES (?, ?, ?, ?)";

            PreparedStatement ps = this.con.prepareStatement(sql);
            ps.setString(1, userBean.getName());
            ps.setInt(2, userBean.getRollno());
            ps.setString(3, userBean.getClas());
            ps.setLong(4, userBean.getMono());
            ps.executeUpdate();
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
    }



// Delete Data
    public void removeUser(int rollno) {
        try {
            String sql = "DELETE FROM student WHERE rollno=?";

            PreparedStatement ps = this.con.prepareStatement(sql);
            ps.setInt(1, rollno);
            ps.executeUpdate();
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
    }



// Edit Data    
    public void editUser(UserBean userBean) {
        try {
            String sql = "UPDATE student SET rollno=?, class=?, mobileno=? WHERE rollno=?";
//          String sql = "UPDATE student SET rollno=?, class=?, mobileno=? WHERE name=?";
//          String sql = "UPDATE student SET name=?, rollno=?, class=?, mobileno=? WHERE rollno=?";

            PreparedStatement ps = this.con.prepareStatement(sql);
            ps.setString(1, userBean.getName());
            ps.setInt(2, userBean.getRollno());
            ps.setString(3, userBean.getClas());
            ps.setLong(4, userBean.getMono());
            ps.executeUpdate();
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
    }



// Viewing Data
    public List<UserBean> getAllUsers() {
        List<UserBean> student = new ArrayList<UserBean>();
        try {

            if(this.con.isClosed()) {
                System.out.println("Connection is closed");
            }
            else    {
            String sql = "SELECT * FROM student ORDER BY name";
            PreparedStatement ps = this.con.prepareStatement(sql);
            ResultSet rs = ps.executeQuery();

                while (rs.next()) {
                    UserBean userBean = new UserBean();
                    userBean.setName(rs.getString("name"));
                    userBean.setRollno(rs.getInt("rollno"));
                    userBean.setClas(rs.getString("class"));
                    userBean.setMono(rs.getLong("mobileno"));
                    student.add(userBean);
                }
            }
        }
        catch (SQLException e) {
            e.printStackTrace();
        }

        return student;
    }




    public UserBean getUserById(int rollno) {
        UserBean userBean = new UserBean();
        try {
            String sql = "SELECT * FROM student WHERE rollno=?";

            PreparedStatement ps = this.con.prepareStatement(sql);
            ps.setInt(1, rollno);
            ResultSet rs = ps.executeQuery();

            if (rs.next()) {
                userBean.setName(rs.getString("name"));
                userBean.setRollno(rs.getInt("rollno"));
                userBean.setClas(rs.getString("class"));
                userBean.setMono(rs.getLong("mobileno"));           }
        }
        catch (SQLException e) {
            e.printStackTrace();
        }
    return userBean;
    }
}